Organic EL devices as luminescent devices with high-speed response and high efficiency have been intensively investigated for their application (see Macromol. Symp. 125, 1-48 (1997), for example).
A copper coordination compound can be produced at a relatively low cost due to inexpensive raw materials, and low-cost and high performance organic EL devices can be obtained when performance of the copper coordination compound is fully utilized.
Organic EL devices using copper coordination compounds are disclosed in Japanese Patent No. 2940514 and Advanced materials 1999 11 No. 10 p. 852 Y. Ma et al. However, these EL devices have remarkably low luminescence efficiency, and these documents have insufficient description of device efficiency. It is difficult to consider that the properties of the copper coordination compounds are fully exploited. Thus, these EL devices do not have enough performance to be used for displaying or lighting.
In addition, a luminescent material of a copper coordination compound used in Advanced materials 1999 11 No. 10 p. 852 Y. Ma et al. has a molecular weight of 1,600 or more, and its molecular weight is so large that the material has inferior sublimation, thus making the material unsuitable for vacuum evaporation.
Further, copper coordination compounds having the same structure as some of the compounds used in the present invention are disclosed in Journal of chemical Society Dalton Transaction 1991 p. 2859; Journal of Chemical Society Dalton Transaction 1983 p. 1419; and Journal of Chemical Society Dalton Transaction 2001 p. 3069, but there is no description concerning luminescence therein.
In Journal of American Chemical Society, 2003 125(40) p. 12072, there is a description of a trinuclear copper coordination compound different from the copper coordination compound of the present invention. The compound described therein has luminescence property, and application of the compound to an organic LED is suggested therein. The distance between copper atoms in the molecular of the compound is about 3.22 Å, and interaction between copper atoms is not strong. This trinuclear copper coordination compound can be vapor-deposited, but has inferior luminescence property (efficiency) and stability for a device.